Double reheat compound turbine powerplant



Oct. l1, 1960 E. H. MILLER 2,955,429

DOUBLE REHEAT COMPOUND TURBINE POWERPLANT Filed July le, 1957 UnitedStates Patent O DOUBLE REHEAT COMPOUND TURBINE POWERPLANT Edward H.Miller, Rexford, N Y., assignor to General Electric Company, acorporation of New York Filed July 16, 1957, Ser. No. 672,201 3 Claims.(Cl. 60-73) This invention relates to elastic luid turbine powerplants,particularly to very large capacity compound steam turbines making useof steam at supercritical pressure and reheating at least twice to atemperature on the order of the initial inlet temperature.

As the cost of fuel has risen higher and higher, powerplant designershave searched diligently for the best arrangement for extremely largecapacity turbine plants representing the optimum combination of lowmanufacturing cost, simple construction and convenient arrangement ofthe piping connecting the various elements of the turbine with the steamgenerator and reheaters, with simplified foundation and condenserarrangement, and lending itself to a neat, symmetrical station layout.

As lthe demand for improved thermal eciency has increased, an increasingnumber of large steam turbine plants have been designed to employ thereheat principle, in which the motive fluid is returned to the boilerfor reheating, at least once in its trip through the turbines,to atemperature which may be on the order of the initial inlet temperature.A further step has been to increase the pressure level `at which theplant operates, and steam pressures have now risen into thesupercritical pressure region, roughly above 3500 p.s.i.a. It thenbecomes advantageous to go to a double reheat arrangement, in which themotive fluid is reheated twice to the initial inlet temperature. Thisinvolves a substantial amount of piping connecting the respectiveturbine components with the steam generator and reheating devices. Ittherefore becomes important, both from the standpoint of complexity andrst cost and from the standpoint of maintenance, that the pipingarrangement be as simple and symmetrical as possible. If the designerldoes not exercise care, such a compound double reheat plant may havecertain turbine casings which are comparatively simple, while themajority of the piping connections are concentrated on other casings.This makes the design problems exceedingly dii'licult, and maintenancecan be troublesome and expensive on those turbine casings which carrythe majority of the piping connections. Also, the size and cost of thebuilding required to house the turbine assembly may be substantiallyincreased if several turbine sections are arranged on a common shaft sothat the combined machine becomes of excessive length.

Accordingly, an object of the present invention is to provide animproved double reheat compound steam turbine arrangement Yin which thevarious turbine sections are divided evenly into two groups or elements,with a major portion of one group being identical in construction to thecorresponding components of the other group.

A further object is to provide a two-element compound turbine-generatorplant in which each element generates power output roughly equal to thatof -the other, so that identical generators can be employed, and furtherfacilitating arrangement of the station layout since the overallconguration of -the two elements is very similar.

Patented Oct. 11, 1960 A still further object is to provide an improveddouble reheat compound turbine arrangement in which a roughly equalnumber of steam conduit connections are required to each of two turbineelements, thus simplifying the piping and connections to the turbinesand achieving optimum accessibility of the piping and turbine sections.

Another object is to provide a large capacity compound turbinearrangement requiring no crossover pipe connecting directly between oneelement and the other, thus reducing the governing problem whichotherwise results when a long, large diameter crossover pipe contains asubstantial volume of uncontrolled steam which may under certainconditions of operation tend to overspeed certa-in of the turbinesections.

ther objects and advantages will Vbecome apparent from the followingdescription taken in connection with the accompanying drawing, in whichthe single igure represents an improved double reheat compound turbinepowerplant in accordance with the invention, the two turbine elementsbeing shown partly in section, and the piping land steam generatingequipment being shown in purely diagrammatic form.

Generally stated. the invention is practiced by dividing the variousturbine expansion sections between two independent shafts, each coupledto drive a separate generator, and corresponding turbine sections oftherespective elements being identical except for the highest pressuresection of each element, the design and arrangement of these highestpressure sections being such that the total output of each turbineelement is roughly the same, both at part load and at full loadoperation.

Referring now more particularly to the drawings, the invention isillustrated as `applied to a very large capacity double reheat steamturbine plant having a number of expansion turbine sections grouped ontwo independent shafts. The rst turbine element includes a maximumpressure section 1, an intermediate pressure section 2, and `a lowpressure sect-ion 3, having a common rotor driving a generator 4. Thesecond turbine elemen comprises the high pressure section 5,intermediate pressure section 6, and low pressure section 7, connected-to drive generator 8. The steam generating `and reheatiug componentscomprise Ia. suitable boiler feed pump shown diagrammatically at 9, asteam generator 10, a rst reheater 11, and a second reheater 12. The4low pressure turbine sections 3, 7 exhaust to separate condensers 3d,7d, or to a common condenser (not shown), from which condensate isreturned by way of suit-able feed water heaters (not shown) to the feedpump 9. The valve means controlling the ilow of motive fluid includesstop valve means indicated diagrammatioally at 10b in the maximumpressure steam supply conduit 10a, and suitable control valve mechanismillustrated diagrammatically at 10c, located closely adjacent the inletto the maximum pressure section 1. Partly expanded steam leaves themaximum pressure section 1 through conduit 11a and after being reheatedin the rst reheater 11 is supplied by conduit 11b to the high pressuresection 5 of the secondary turbine element, this flow being under thedirect control of the reheat stop valve 11C and reheat intercept valve11a. Here again, it will be observed that the intercept valve 11d islocated closely adjacent (in this case directly on), the `casing of thehigh pressure section 5. Steam exhausted `from section 5 passes by wayof conduit 12a to the second reheater 12, thence by way of conduit 12bto both the intermediate sections 2, 6. This ow is controlled by thesecond reheat stop valves 12e and the respective intercept valves 12d,12e located on the respective casings of turbine sections 6, 2.

As will be apparent from the drawing, the low pressure sections 3, 7 areeach actually triple fiow units. That is, part of the steam exhaustedfrom the intermediate pressure sectionl, roughly a third of the fiow,passes directly through the immediately adjacent low pressure section3a. The remaining two-thirds of the iiow goes by way of the crossoverpipe 2a to the com mon inlet chamber of the opposed iiow low pressuresections 3b, 3c. Similarly, after passing through the intermediatepressure section 6, the steam flow in the second turbine element dividesthree ways, passing through the low pressure section 7a and the opposedflow low pressure sections 7b, 7c, in parallel. Thus the lowest pressureportion of this powerplant is actually a six-flow arrangement, sincethere are six substantially identical low pressure expansion sections inparallel fiow arrangement.

With this arrangement, it is possible to design both turbine elementsfor operation at 3600 r.p.m., as contrasted with other cross compoundturbine plants in which it has been considered necessary to employ one3690 r.p.m. element `and one 1800 r.p.m. element, in order to obtain therequisite aggregate flow path area for the low pressure steam. Thus withthe present invention it becomes feasible to make the. two turbineelements completely identical in construction throughout a major portionof the apparatus. Specifically, it will be observed from the drawingthat the low pressure turbine sections 3, 7 and the two intermediatepressure sections 2, 6 are complete duplicates. It will be apparent fromthe drawing that these elements represent the major `fraction of theapparatus employed. It is, of course, of extreme importance from thestandpoint of low `manufacturing cost, and from the standpoint offurnishing and stocking spare parts for maintenance during the life ofthe machine, that such a large portion o-f the apparatus can be exactduplicates.

yIn order to equalize the power output of the two turbine elements, itis necessary that the maximum pressure section 1 and the high pressuresection 5 employ a different number of stages of expansion.Specifically, the design and number of stages in the high pressuresect-ion is so selected that the power output of this section is asclose as possible to that of the fewer expansion stages contained in themaximum pressure section 1. Thus, since the respective -intermediatepressure sections and low pressure sections are complete duplicates, itfollows that the total capacity of the first turbine element will besubstantially identical to that of the second turbine element. This inturn means that the generators 4, 8 may be duplicates. With thisarrangement, the total power output of the plant is divided roughlyequally between the first and second turbine elements, both `at partload opera-tion and at full load. This greatly simplifies the electricaloperation of the plant, since the identical generators 4, 8 may bereadily connected together electrically to a common distributionnetwork, without the operating problems which arise when generators ofdifferent speed or of substantially different capacities, are connectedto a common distribution network.

A numberl of most important advantages result from this improvedcompound turbine arrangement. Foremost among these is the fact thatthere is no crossover pipe communicating between a higher pressuresection of the first turbine element and -a lower pressure section ofthe second element. This means that there is no steam conduit ofsubstantial length and volume and having no valve means for controllingthis volume of steam when the governing mechanism calls for a suddenload change. Inspection of the drawing will reveal that all conduitswhich contain no valves communicate with the heating devices 11, 12, notwith the other turbine element. Stated conversely, every steam supplyconduit is provided with one or more valve means immediatelyapproximately 105 0 adjacent the connection of the steam conduit withthe turbine section it serves. Thus there is no substantial volume ofsteam uncontrolled by an appropriate valve device, which volume of steamwould be free for uncontrolled expansion through the next lower pressureturbine section in the event of sudden reduction in load output. Thusthe governing problem is very much simplified. It may be noted furtherthat the only uncontrolled crossover conduits are the comparativelyshort conduits 2a, 6a, which communicate between sections of the sameturbine element, not from one turbine element to the other.

Another very important practical advantage lies in the fact that `thefirst and second turbine elements can either be located closely adjacentto one another or at a considerable distance apart, resulting also fromthe fact that all uncontrolled piping communicates with the heatingdevices, not between elements, and there are appropriate control valvesimmediately adjacent the entrances to the respective turbine sections.lf it is desired to locate both elements closely adjacent, they mayconveniently be mounted on a common foundation structure, and may alsobe provided with a single transversely disposed condenser receivingsteam from all six of the low pressure sections. It is of course alsopossible, where desired, to use separate condensers for each element.

lt is also significant that by dividing the turbine expansion sectionsbetween two elements which are so nearly identical, and so very similarin size and external configuration, the .problem of arranging thestation layout is much simplified, as compared with the problemsinvolved in designing a plant having elements of' substantiallydifferent size and configuration. It may be noted that not only thefoundation structure but also the lubricating oil feed and drain pipingmay be entirely or substantially identical on the respective first andsecond elements.

In connection with the simplification of the piping required in thiscompound plant, it is significant to note that the first and secondturbine elements each require the same number of piping connections.That is, each has two steam inlet connections, one connection to areheater, and equal numbers of connections to the condenser.Furthermore, these connections are located in similar positions on thefirst and second elements. This makes for optimum accessibility of thepiping and connections thereof to the turbine casings, and permits asymmetrical layout of the piping to the first and second elements.

By way of example, it may be noted that in a turbine plant of the typedescribed having a total capa-city of 450,000 kw., steam may be suppliedby the steam generator 10 at a pressure of 3500 p.s.i.a. and atemperature of F. The motive fiuid exhausts at about 970 p.s.i.a. and720 F. into the conduit 11a. The temperature of the steam supplied byreheater 11 through conduit 11b may again be on the order of l050 F. Thepressure in the second reheat conduit 12a may be on the order of 320p.s.i.a. and at a temperature of about 780 F. The discharge temperatureof the steam supplied by reheater 12 to the conduit 12b may again be onthe order of 1050 F. The steam expands in the low pressure sections 3, 7from about 290 p.s.i.a. to condenser pressure, which may be on the orderof l1/2 inches of mercury, absolute. As noted above, both turbineelements may operate at 3600 r.p.m.

1t will be seen that the invention provides a large capacity compoundturbine powerplant in which numerous stages of expansion are dividedinto sections, the sections being grouped into two elements and arrangedin such a manner that the rather complex piping connections required tothe two reheaters are simplified, there are no long uncontrolledcrossover pipes between elements to create serious governing problems,the design and arrangement of foundation, station layout, and condenserconnections are greatly simplified, and engineering and manufacturingcosts can be reduced by the very substantial extent to which the twoturbine elements are mechanical duplicates.

While only one embodiment of the invention has been describedspecifically, it will be appreciated by those acquainted with the steamturbine art that many substitutions and modifications could be made. Itwill, of course, be appreciated that the valve mechanism and the pipingarrangement is illustrated inpurely diagrammatic form in the drawing andcould take many equivalent forms. The invention may be applicable toelastic fluid turbine plants using motive fluids other than steam. Itis, of course, intended to cover by the appended claims all suchmodifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A compound multiple reheat elastic fluid turbine powerplantcomprising means for generating elastic motive fluid at a first maximuminlet pressure and first temperature, said first maximum pressure beingabove the critical pressure of the fiuid, a first reheater connected toreheat partly expanded fluid to substantially s-aid first temperature, asecond reheater connected to receive still further expanded fiuid andreheat it to substantially said first temperature, a plurality ofturbine uid expansion sections comprising a first turbine element havinga maximum pressure section, an intermediate pressure section, and a lowpressure section with rotors connected together in tandem, and a secondturbine element comprising a high pressure section, an intermediatepressure section, and a low pressure section with rotors connectedtogether in tandem and physically separate from the rotor of said firstturbine element, first maximum pressure conduit means supplying motivefluid from said generating means to the inlet of said maximum pressuresection of the first turbine element, second conduit means supplyingmotive fluid exhausted from the maximum pressure section to said firstreheater, third conduit means supplying reheated motive fiuid from thefirst reheater to said high pressure section of the second turbineelement, fourth conduit means supplying motive fluid exhausted from saidhigh pressure section to said second reheater, fifth conduit meanssupplying reheated motive fiuid from the second reheater in parallel toboth the intermediate pressure sections of said first and second turbineelements, sixth conduit means supplying motive fluid exhausted from theintermediate pressure section of the first turbine element to the lowpressure section of the first element, and seventh conduit meanssupplying motive fiuid exhausted from the intermediate pressure sectionof the second turbine element to the low pressure section of the secondelement.

2. A compound multiple reheat turbine powerplant in accordance withclaim 1, in which the design and number of expansion stages in themaximum pressure turbine section of the first turbine element is suchthat said maximum pressure section has substantially the same poweroutput as that of the high pressure turbine section of the secondturbine element, the second reheat sections and low pressure sections ofthe first and second turbine elements being respectively ofsubstantially identical construction, whereby the total power output ofthe first turbine element is substantially equal to that of the secondturbine element.

3. A compound multiple reheat steam turbine powerplant comprising meansfor generating steam at a first maximum inlet pressure and firsttemperature, said first maximum pressure being above the criticalpressure of the steam, a first reheater connected to receive partlyexpanded steam and to reheat it to substantially said first temperature,a second reheater connected to receive still further expanded steam andreheat it to substantially said first temperature, a plurality ofturbine expansion sections comprising a first turbine element having amaximum pressure section, an intermediate pressure section, and a lowpressure section connected together in tandem to drive a first loaddevice, and a second turbine element comprising a high pressure section,an intermediate pressure section, and a low pressure sectionmechanically independent of said first turbine element and connected intandem to drive a second load device, first maximum pressure conduitmeans supplying motive fluid from said steam generator to the inlet ofsaid maximum pressure section of the first turbine element and includingcontrol valve means adjacent said maximum pressure inlet, second conduitmeans supplying steam exhausted from the maximum pressure section tosaid first reheater, third conduit means supplying reheated steam fromthe first reheater to said high pressure section of the second turbineelement and having valve means adjacent the inlet to the high pressuresection, fourth conduit means supplying steam exhausted from the highpressure section to said second reheater, fifth conduit means supplyingreheated steam from the second reheater in parallel to Ithe intermediatepressure sections of both the first and the second turbine elements andincluding separate control valve means immediately adjacent therespective inlets to said intermediate pressure turbine sections, sixthconduit means supplying steam exhausted from the intermediate pressuresection of the first turbine element to the low pressure section of thefirst element, and seventh conduit means supplying steam exhausted fromthe intermediate pressure section of the second turbine element to thelow pressure section of the second element.

References Cited in the file of this patent UNITED STATES PATENTS1,089,115 Curtis Mar. 3, 1914 2,238,905 Lysholm Apr. 22, 1941 2,504,640Bryant Apr. 18, 1950 2,568,787l Bosch Sept. 25, 1951 FOREIGN PATENTS808,529 France Nov. 14, 1936 216,921 Germany Dec. 8, 1909 518,784Germany Feb. 19, 1931 3,641 Great Britain June 8, 1911 19,106 GreatBritain Oct. 14, 1909 256,209 Great Britain Oct. 21, 1926

